In vitro incorporation studies with human uterine tissues have demonstrated an increased reduction of testosterone to its physiologically more active metabolite, dihydrotestosterone by uterine neoplasms. We have also observed the presence of a saturable cytoplasmic binding component with a high affinity for dihydrotestosterone. Limited data also suggest that some uterine neoplasms contain a higher concentration of this binding element. Since 5 reduction and specific cytoplasmic binding of the reduced androgen are classically crucial steps required for the expression of androgen effects, these preliminary data suggest a physiologically significant role for androgen in the metabolism of human uterine neoplasmas.